Building Better, More Energy-Efficient Walls

You probably don’t give a lot of thought to wall construction, but here at steveworks, we give it A LOT of thought. In fact, there are many ways to build a wall, but not all of them are…

  1. Up to official Massachusetts code standards
  2. Energy efficient
  3. Keeping best “green building” practices in mind
  4. Using low carbon footprint materials  

Rather than bore you with the details on the many types of wall construction available, I’d like to focus on what we prefer to use when we work on a remodeling project. Massachusetts code now requires R-20 insulated walls (previously it was R-13). Let’s stop and review what the R-value means in case you aren’t sure: R-values represent resistance to the flow of heat; the higher the R-value, the greater the resistance and the insulating value.

Today, builders are required to build R-20 insulated walls with exterior insulation. How you get the R-20 is up to the builder, but there are ways to do it correctly, and ways to totally screw it up. And if it does get screwed up the result is moisture in the walls, which eventually leads to mold and rot.

This is a photo of an energy retrofit we did a few years ago.  We took advantage of the fact that the home was going to be re-sided.  You can’t see the first layer of insulation: dense-pack cellulose insulation which was blown into the wall before the foam was installed from the exterior.  This brought us to R-13.  Next, on the exterior we installed an inch of rigid foam (the Energy Shield you see in the photo) which is rated at R-6.  Now we had our R-20 wall.  We could easily install a thicker layer of foam to get a high R-value if we thought it was necessary, but we had more energy-efficient tricks up our sleeve. We taped the joints between the sheets to air seal the wall. The result: no breeze coming through the wall.  You may have noticed the 1×3” strapping in the photo over the Energy Shield. The strapping is there to provide an air gap between the siding and the foam.  This serves two purposes: 1) it allows any trapped moisture to drain out behind the siding so the wall assembly stays dry and 2) it allows the air temperature behind the siding to be the same as the exterior.  This helps the siding stay “stable” and prolongs the siding material and paint. Above the porch you can see a completed section.  Hardie Board siding was used as it’s a great alternative to cedar siding for cost and durability. Plus, it comes factory-painted with a 15-year warranty!

If you read our previous blog you’ll know that we’re moving away from using foam products because the energy and chemicals needed to produce the foam is carbon intensive. As lower-carbon alternatives become more cost-competitive, we plan to use them more and more in the future. Bottom line: we’re always looking for new ways to reduce the environmental impact of each project, so our approach to walls is certain to change as new technology and “green” alternatives become available.

This photo illustrates a product that been around for a few years. It combines plywood and a vapor barrier (the green, outer layer) that is designed to let moisture OUT rather than IN (that’s the green applied layer).  We often use this product in combination with a bonded foam layer (instead of a separate installed layer of exterior) which we fasten directly to the framing.

Huber Wood, a product we often use, created a great video about the insulated wall system. The Huber “Zip System” was designed to provide continuous insulation (meaning, the heat doesn’t leak out between the seams of the panels) plus a moisture barrier as well as an air barrier (for greater energy efficiency). In essence, it keeps the heat in your home, while keep moisture and drafts out. The house is sealed up tight!